1. Field of the Invention
The present invention relates to an exhaust valve suitably usable in a sphygmomanometer and a sphygmomanometer using the same.
2. Description of the Related Art
Blood pressure is extensively used as a value reflecting the state of circulatory organs, and various sphygmomanometers have been developed. Although blood pressure is measured on the basis of various principles, sphygmomanometers using a so-called oscillometric method is widely used.
The oscillometric method avascularizes a measurement portion such as an extremity by externally pressing it, detects oscillations from the blood vessel (artery) while gradually lowering the pressure, and measures the blood pressure on the basis of the oscillations and pressure.
A sphygmomanometer based on the oscillometric method generally presses a measurement portion by using a cuff. To increase the pressure of the cuff, the sphygmomanometer supplies a gas such as air to an air bag inside the cuff. To reduce the pressure, the sphygmomanometer exhausts the gas from the air bag by opening an exhaust valve.
As described above, when a sphygmomanometer of this type is used, the pressure must be gradually lowered from the avascularized state. It is important to maintain the exhaust rate (exhaust flow rate) ideally constant, and, in practice, within a predetermined range centering around a target value.
For this purpose, reference 1 (Japanese Utility Model Publication No. 56-41687) has proposed an exhaust device having an exhaust nozzle extending through the core of a solenoid, and a valve membrane that opens and closes by the operation of the solenoid. This exhaust device adjusts the exhaust amount by an electric current supplied to the solenoid.
Also, reference 2 (Japanese Patent Laid-Open No. 59-141934) has proposed an arrangement in which in an exhaust amount control valve uses a solenoid positioned so as to be cooled by the exhaust gas, in order to suppress the influence which the heat generated by an electromagnet in the solenoid has on the physical properties and flow rate of the valve.
In the arrangement described in reference 1, however, the exhaust nozzle extends through the core of the solenoid. This inevitably increases the size of the solenoid. Also, the structure is not hermetically sealed even while the valve membrane is pushed against the nozzle opening by supplying an electric current to the solenoid. This makes it difficult to stably adjust particularly the initial flow rate.
The structure described in reference 2 cools the solenoid by using the exhaust gas. Therefore, the solenoid is positioned such that its longitudinal direction is perpendicular to the exhaust channel. This complicates the mechanism that opens and closes the valve.